A hairdresser whose death during the final stages of the London Marathon led to more than £1m being donated to charity had taken an amphetamine-like drug which she had bought legally on-line, an inquest heard today.

There were calls for greater regulation of over-the counter stimulants in the wake of the tragedy last year when Claire Squires, 30, collapsed in front of horrified spectators just a mile from the finishing line in Birdcage Walk. Runners in future marathons will be warned of the possible dangers of legal stimulants as a result of the findings.

Coroner Dr Philip Barlow said the keen athlete was not a regular user of the supplement Jack3D, but that significant levels of its active ingredient, 1,3-dimethylamine (DMAA), were found within her system.

Ms Squires from North Kilworth, Leicestershire, had purchased the popular supplement legally over the internet in advance of the race and planned to take it to boost her energy when she became tired, her boyfriend told the inquest at Southwark Coroner's Court.

Jack3D was outlawed from uncontrolled sale in Britain by the Medicine and Healthcare products Regulatory Agency (MHRA) in August last year following reports of high blood pressure, stroke and even deaths among users in the United States and Australia. Experts found that it contained active agents capable of altering human physiology and ruled that it was a de facto medicine.

Describing Ms Squires as “a very dedicated and well-motivated person”, Dr Barlow said he hoped the case would highlight the dangers associated with the drug.

“She had taken a supplement containing DMAA which, on the balance of probabilities, in combination with extreme physical exertion, caused acute cardiac failure, which resulted in her death,” he said while recording a narrative verdict.

Ms Squires, who had completed the London Marathon two years previously, was described as a fit and healthy woman during the inquest.

She had aimed to beat her personal best and finish the race in less than four hours raising £500 for the Samaritans - a figure which soared to more than £1m in the wake of public sympathy over her death.

Boyfriend Simon van Herrewege said Ms Squires had been building up steadily to the race training five times per week.

He said she put a scoop of Jack3D into her water bottle and intended to use it to give her a “caffeine-like” energy boost when she “hit the wall” – a term used by marathon runners to describe the point where the body’s carbohydrate reserves are depleted and fat begins to be broken down resulting in a loss of performance and extreme fatigue.

Speaking after the inquest Mr van Herrewege said: “Claire would never ever have taken anything that would cause her harm or even worse risk her life.

“She innocently took a supplement which at the time was entirely legal and widely available on the high street and somewhat worryingly apparently used by so many others.

“It is clear that there needs to be far better supervision of the so-called health foods and supplements industry so that no more tragedies like this happen again causing other families to have to go through what we have been through this past year.”

Andrew Kicman of the drug control centre at King's College London said the powder was widely used. ”I suspect that many, many people who use supplements such as Jack3D are not aware of what the supplement is,” he said.

“It is not illegal to take it but if you are doing competitive sport it may be against the rules of the sporting association. There would be no reason for a runner in the London Marathon not to take it provided they are not an elite runner,” he added.

Paramedic Donna Tucker, who was watching the race, ran to help when she spotted Ms Squires slow, stagger and collapse.

“She appeared to have a mild seizure that lasted about five seconds,” she said. Despite receiving cardio pulmonary resuscitation at the scene she was taken to St Thomas's Hospital where she was pronounced dead an hour later.

A post mortem examination revealed an unusual amount of blood in her lungs, possibly as a result of having taken the stimulant.

Jack3D is still being sold on Amazon but the DMAA has been taken out of it, the inquest heard.